There is a projection display device that includes two light sources to acquire light of high luminance. This projection display device enables acquisition of light of high luminance by synthesizing light emitted from the light sources.
FIG. 1 schematically shows an internal mechanism of the projection display device that includes the two light sources. The projection display device includes two light sources 401a and 401b located side by side. Two light sources 401a and 401b are set in the same direction.
In the projection display device, first, lights from light sources 401 and 401b enter color wheel 402. Color wheel 402 is a disk-like member that includes a translucent color filter. The color filter is divided into a plurality of color separation areas in a circumferential direction. Each color separation area selectively allows transmission of only light of a wavelength that becomes red, green or blue. Color wheel 402 can rotate around a central axis. By rotating color filter 402, the color separation areas through which the lights emitted from light sources 401a and 401b are transmitted are continuously changed.
The lights transmitted through color wheel 402 enter one of the ends of rod lenses 404a and 404b. Rod lenses 404a and 404b are rod-shaped glass members rectangular in section. The lights that have entered one of the ends of rod lenses 404a and 404b are transmitted through rod lenses 404a and 404b to exit from the other ends. The lights are totally reflected repeatedly on side faces of rod lenses 404a and 404b during transmission from one of the ends of rod lenses 404a and 404b to the other ends. Thus, luminance distribution is made uniform.
The lights that have exited from rod lenses 404a and 404b are transmitted through condenser lenses 405a and 405b, and then enter condenser lens 406. The lights transmitted through condenser lens 406 are reflected by planar lens 407, and then enter condenser lens 408.
The lights transmitted through condenser lens 408 enter digital micromirror device (DMD) 409. DMD 409 is an image forming element having many mirror elements attached on a semiconductor memory cell to be switched on/off individually based on image signals. The lights that have entered DMD 409 and that have been reflected by the mirror elements of DMD 409 to be modulated are magnified and projected on a screen (not shown) from projection lens 411.
In the projection display device, the lights that have exited from rod lenses 404a and 404b gradually approach each other while they are sequentially transmitted through condenser lenses 406 and 408. The lights overlap each other to become almost one light flux, and enter DMD 409. Thus, in the projection display device, the lights emitted from two light sources 401a and 401b are synthesized through condenser lenses 406 and 408. This enables displaying of one image on the screen.
However, in the projection display device, the lights emitted from light sources 401a and 401b enter positions opposite each other sandwiching the central axis in the color filter of color wheel 402. Color wheel 402 is always required to set the light emitted from light source 401a and the light emitted from light source 401b similar in color. Thus, the color filter of color wheel 402 must include a pair of opposing color separation areas sandwiching the central axis for each color. In other words, the color filter of color wheel 402 must be divided into six color separation areas in the circumferential direction.
In the projection display device, when the lights emitted from light sources 401a and 401b are transmitted through the color separation area of the same color, light of red, green or blue can be acquired. However, when the lights emitted from light sources 401a and 401b are transmitted over a boundary between the two color separation areas, two colors are mixed. Light of a color made by mixing the two colors is not used for displaying an image. Thus, during incidence of the lights that are emitted from light sources 401a and 401b through two color separation areas, the mirror elements of DMD 409 are all turned off.
As described above, in the projection display device, while the number of colors of light necessary for displaying the image is three, namely, red, green, and blue, the color filter must be divided into twice as many as the number of colors, namely, six color separation areas. The number of times of turning off all the mirror elements of DMD 409 per rotation of color wheel 402 is three when there are three color separation areas. However, the number is six in the projection display device. As a result, in the projection display device, the lights emitted from light sources 401a and 401b cannot be efficiently used for displaying the image.
FIG. 2A is a configuration view schematically showing an internal mechanism of a projection display device including two light sources and configured to transmit lights emitted from the light sources through the same color separation area of a color filter. The projection display device shown in FIG. 2A is similar in configuration to the projection display device shown in FIG. 1 except for a configuration described below.
The projection display device includes triangular prism 503 that includes mirror-coated surfaces 503a and 503b. In the projection display device, lights emitted from light sources 501a and 501b are reflected by surfaces 503a and 503b of triangular prism 503, transmitted through positions of a color filter of color wheel 502 approaching each other, and then enter one end of rod lens 504. In the projection display device, therefore, the lights emitted from light sources 501a and 501b can be transmitted through the same color separation area of the color filter. Thus, the color filter is only required to be divided into three color separation areas equal to the number of colors of light necessary for displaying an image.